Noun. A term that can be interjected into any situation to describe something that is indescribable. Usually derogatory in connotation.

Conceived one evening (In July of 2006) out of boredom and laziness, the term 'nasty unicorn' was first used by Joshua Mosley to describe his feelings towards a wet napkin. When the napkin in question was thrown on his face, he told the assailant, "You need to quit with your nasty unicorn!" The term has been frequently used throughout Treutlen County since then.

Can be used acronymns, i.e.;
STNUU- Shut the Nasty Unicorn up
WTU- what the unicorn?!

Although no examples can be given due to its indescribable nature, the term 'nasty unicorn' is most often used in a sentence as a noun in response to something horrific and/or disgusting;